The present invention relates to sports racquets having strings, for example, tennis racquets, squash racquets, badminton racquets, and racquetball racquets.
Aside from strength and durability, weight and weight distribution have always been among the most important physical characteristics in a sports racquet. Tennis is a collision sport, as are other racquet sports, and the momentum and inertia of a racquet upon ball impact are directly related to the power and sweet spot size.
Over the past fifteen years, the speed of the game has changed with bigger, more powerful players resulting in higher ball speeds However, the mass of the ball and court size have remained the same, resulting in shorter rallies and higher impact loads imparted by the ball to the racquet. Over this same time period, due to improvements in materials and manufacturing technology, racquet weights have decreased drastically. In the case of tennis racquets, racquet weights have decreased by over 140 grams, from a typical strung weight of 360 grams to present day strung weights as low as 220 grams.
Lighter racquets tend to be more maneuverable and thus, in such respect, would appear to be better suited to a faster game. However, lighter racquets are less stable, which has a doubly negative effect in the case of any balls which do not land exactly at the racquet's center of mass. First, the racquet tends to twist, either about the longitudinal axis (in the case of balls which land off-axis), or about the center of mass (or both), more than a heavier racquet hitting the same ball. Second, because faster ball speeds mean greater impact momentum, the twisting force will be magnified compared to a heavier racquet. Thus, lighter racquets tend to be harder to control, and for such reason, professional tennis players continue to use heavier racquets.
In the past, proposals have been made to improve the stability of the racquet. For example, Wilson Sporting Goods markets racquets with a "Perimeter Weighting System", in which small weights are placed at the 3 o'clock and 9 o'clock locations on the racquet head. These weights increase the polar moment of inertia, and thereby improve the resistance to twisting on side-to-side off center hits, but do not improve the stability about the racquet's midpoint.
Nikonow U.S. Pat. No. 1,539,019 discloses a racquet which uses a lightweight handle and in which weight is shifted to the tip region in order to advance the location of the center of percussion. Removing weight from the handle and shaft, and shifting such weight to the head, has two disadvantages. First, the racquet becomes head heavy and thus less maneuverable. Second, the longitudinal stability of the racquet about its midpoint is reduced. Thus, when balls land on the string bed above or below the center of percussion of the racquet, the handle will have a greater tendency to kick out of or towards, respectively, the player's hand. In addition, this weight distribution does not improve the polar moment of inertia of the racquet.
Other companies have tried various weight distribution schemes, all with certain drawbacks.